1. Field of the Invention
The present invention relates to a method for producing spinel fine powders having high purity.
The fine powders consisting of a single phase of spinel solid solution composed of aluminum and magnesium oxides shown by the following general formula EQU MgO.xAl.sub.2 O.sub.3
wherein x is 1-1.5, are useful as the raw material for producing dense and uniform spinel sintered bodies, such as transparent spinel sintered bodies and the like.
2. Description of the Prior Art
The following prior methods have been proposed for producing such spinal fine powders.
(1) Producing spinel through a solid phase reaction of aluminum oxide with magnesium oxide wherein the formed spinel is pulverized.
(2) Forming a mixture of an aluminum salt and a magnesium salt that is subjected to pyrolysis.
(3) Adjusting the pH of an aqueous solution of an aluminum salt and a magnesium salt to cause co-precipitation.
However, the above described solid phase reaction method (1) is apt to cause unevenness in the composition of the formed phase and it is difficult to obtain fine powders having a uniform composition. Furthermore, the activity of the particles is lowered due to treatment at high temperature, and sintering of the formed powders is difficult.
The above described salt decomposition method (2) has a drawback in that anions remain in the formed fine powders as an impurity.
The above described co-precipitation method (3) has a drawback in that the adjustment of pH is difficult and it is impossible accurately to control the composition.
It has been known in the sintering of spinel, to add a slight amount of LiF in order to promote densification at low temperature, but the addition and dispersion of LiF has been heretofore carried out through mixing by means of a ballmill, with a result that the dispersion cannot be satisfactorily effected and nonuniformity is caused in the sintered body.